Dual crystal unit



Dec. 14, 194s.v R J, JAHRUNG 2,456,421

DUAL CRYSTAL UN IT Filed March 15, 1948 (mnu.

UNIT

gmc/wm PoERT J: Mp4/N6 AToRNEY 2 sneets-shet 2 Patented Dec. 14, 1948DUAL GRYSTMI- Robert-Jr. .Iahrling .IamaeaN; Ywassg-,norr to PremierCrystal. Laboratnxieg. Incorporated,

New York,.N. Y.

Applwienmmn. 15, lamentiamo. intesa.y

(ci. 1v1-327.),

7.01aims,

'1-'1 Thisfirrventimrrelates. opiezoL-electric crystal assemblies,.and-moreparticularly Vto a crystal unit adapted* .tcrr provide y azstable low f when connected s to a'. suitable oscillator circuit..

A main; obiecti of 'f the:V invention isA` tof-provide anovel.: and;improved-crystal iinitiof*` theY dual f ty-,pe

whiehisr especially adaptedfor'nse-with dual oscillatonsY totproducefa;stable .beat frequency, such as: aniaudio frequency, saidunit havingself-cont'ainedffmeanst fior.v adjusting they `resul-tant beatfrequemicyrby adjustingfthe frequency-ot one crystmL. f

1`..fm:t1"1er.r object of. the a invention is tty-provide am;Iimp1'erred?r dual. crystal assembly embodyingmeans: for yadustirxgv thebeat frequency obtainahlenfrmn oscillators controlled byfthe respectivecrystals when said oscillators are heterodyned; the: ass errzbly.lbeing; very simple in construction, compact, in .size; and `relativelyinexpensive to manufacture.

Astilifiurther object ofy the invention is to pro-- vida arr improvedidual.' crystal. assembly for use with; heterodyning; oscillators toprow-ide a` stable beat. frequency,y sncl'r audio frequency,v theassembly being?r readilyadjnstable.- so-that an eX-- act beat frequencyvalue may be @tained-.when the unit is employed asabove-deseribed,-the-ad justing. meansfbeing-vaccessible from outsidethe unit, the unit. beingveryrugged in` construction andinvolving, onlyasmallniimber. of parts.

lurther objects and advantages of. the inyen.- tion-wilt.become-apparent'from the following description. and: claims, and. from the.accompanying drawings, wherein: f

Eigure 1. is. a transverseyertical. cross-sectional View` takenthroughadual.I crystalnnit vconstruct.- ed in. accordance with thepresentinvention, said View being. takenoxiline` I-l of .Figure 2..

Figure 2: is a horizontal cross-sectional, View. taken.y throngh.- theunit oirigure. l. onthe lin theref.

Figure 4% is-.a.,s.che-matic.-diagram illustrating-arst method; ofconnectingthecomponent. ele` ments of.thecrystalsy assembly ofiliigure;1..

Figure. 5- isf a schematic diagran-r.ilhistratimzc,` a, second, methodof ccnneeting-v the componenty elements of the 1 crystal assembly of-Elgure.

Fig-uref Ghisa perspective-view.' of thegronndA plate employed in thecrystal inrity of. Figure-11:. show-ing; additionaly elements vofthe,assembly aecured'theretor f f Figure `71: is r an.- enlarged fragmentarycross-sec.- tionaLdeiail-view. takerri line-'l--Ji-of Eigurfea.

vllig-iir-e- 8 isk ay block diagram illustratingv the mammaire-.whichthe. crystal uni-t of Figure-'Lis employed.- Withrhetercdyni-ngoscillators. to., pro-- duce-1y aidesired stable. beatirequency.,

Rotating, to.-y the drawings, the housing of, the crystal: .mm1-isdesignated generally.r at Il. and comprisesa.- base-.plate- I?. otsiiiitable;ifnsaulating matesiaanda cover member I-3, also,I ofinsulating material,.w-lch securedtothe base plataby screwsI-,ll'-whiclr nass upwardly through-.baseplate t2 antil`aretlzireaded,into. the edge. portions., oi the.- correr'mernilaer: I3.Designated. at Ii` is a. vertical. metal plate.- fitting closely, betxiveen.v the` opposite inside wall-,f surfaces ofcover; memberI I.;plata. Ifbeng formed. with a. horizontal `mbt-.- tom ,flange I6..Designated at Il; is a .pronti havingatlireadedshank portioni whichpassesunwardlgythroughfbase plate I2! and. through. flange It. Prong,L1. isiormedwith a hexagonalcoliar I9 which, bears onthe, bottom surfaceof. .basev plate-l 2: and has-threaded; on. the shank'. portion Ieanut.2,0..which,bears on flange IB, whereby nlate. I5..-.is-tightly securedto platev l2..and.-prong I1 affords-.ana electrical connection. thereto.

Designated. at,` 2JY a variable. trimmer con.- denser.- ai,wel]-knownconstruction,y such. as Cen.- tralala part 823-AN-madebyCentralabf aDivison oi Globe-Union. Inc., Milwaukee... Wisconsin, saidcondenser being characterized by havinga. `hex-- agonal stud. 22.projecting from itscentral. portion., inwhichisthreaded. the. trimmeradjusting screwA 2.1 Whiclrmay berot-ated by a screw driver towadjust.thezcapacitanoeof. the. condenser. Proiectingjroro thehody of,A the.trimmer. 2 I. on opposite. of. the-stud. 22 are square. metal, studs.Z4, 2A', rireteito. the body ofthe trimmer, said studs 24,.. 24.. being.tapped. to receive fastening sereine?. VDesignated; atl, and 2li. arevertioaldn: sulatingbars-oiu substantial.. thickness .and similar.in-.shape` Bars 7.5.. and-,2.6 are formedat their lower ends withrespective opposingA arms,"

2a .at1 theirY intermediate portions with respecopposina arms 29 and30.-. Passing through arms. la and.. imv and. through vertical.. plate.Il

' are fastening screws 3 I, 3I which threadedlyf. en,-

gage the trimmed. studs 24,. 24, and. secureA the-respec-.tivebars, 25,.26 to the.. plate member I5, on one. side. thereof. andthe, trimmercondenser 21., toy saidfplate memberonthe othersidethereof. Theenten-.surfaces ofthe bars..25. and. 2E are. substanrtallyilushwiththe-edges-.o plate member. l5 ao thatsaidoutersurfacesaarealso closely fittedlin.-

side .wanner-.member t3.

.Rlatemember. I5- aformed. with. a.; circular:

stud being therefore positioned between the inwardly extending arms 29and 30 of the bars 25 and 26. Threaded into the wall of cover member I3in axial alignment with trimmer screw 23 is a removable plug 33. Whenplug 33 is unscrewed from the wall of cover member I3, a screw drivermay be inserted into the unit to engage the trim.. mer screw 23 foradjusting the capacitance of trimmer 2|.

Arms 29 and 30 define with the upper portions of bars 25 and 26, platemember l5, and the top wall of cover member I3 a rectangular cavity.Positioned in the cavity adjacent plate member I is a first crystalplate 34. Positioned adjacent the side edges of crystal plate 34 arevertical spacer bars 35, 35 of insulating material, such as glass,slightly greater in thickness than crystal plate 34. Bearing on thespacer bars is a metal electrode 36 which closely fits into the cavity,said spacer bars providing a small air gap between the electrode 36 andthe crystal plate 34. Secured to the bars and 26 is a metal strap member31 which bridges the cavity in which the crystal plate 34 and theelectrode 36 are contained. A coiled spring 38 is positioned betweenelectrode 36 and strap member 31, whereby electrode 36 is firmly held inabutment with the spacer bars 35.

Arms 21 and 28 define with arms 29 and 30, the lower portions of bars 25and 26, and plate member I5, a second rectangular cavity. Positioned insaid second cavity adjacent plate member I5 is a second crystal plate39. Positioned adjacent the side edges of crystal plate 39 areadditional vertical insulating spacer bars 35, slightly greater inthickness than plate 39. An electrode 46 is fitted in said second cavityand bears on the spacer bars 35, 35 therein. A second strap member 4I issecured to bars 25 and 26, which bridges said second cavity. A coiledspring 42 is positioned between electrode 40 and strap member 4I,whereby electrode 40 is rmly held in abutment with the spacer bars 35,35 in the second cavity.

Designated at 43 and 44 are additional prong members secured to basemember I2 parallel to prong member I1, said prong members havinghexagonal collars shown respectively at and 46 and threaded Shankspassing through base member I2, on which respective nuts 41 and 46 arethreaded.

The crystal plates 34 and 39 are matched in frequency and have identicaltemperature-frequency characteristics. The assembly may be wired ineither the manner shown in Figure 4 or the manner shown in Figure 5. InFigure 4, crystal electrode 36 is connected by a wire 49 to prong 43 andcrystal electrode 40 is connected by a wire 50 to prong 44. The trimmercondenser 2| is connected in parallel with crystal 34, one terminal ofthe condenser being connected to plate member I5 and the other terminalthereof being connected to the prong 43.

In Figure 5 the trimmer condenser 2| is connected in `series withcrystal 34 instead of being connected in parallel therewith as shown inFigure 4.

Figure 8 discloses the manner in which the unit is connected to anexternal circuit in order to provide a desired audio frequency outputsignal. The circuit comprises a first oscillator 5| and a similar secondoscillator 52. The prongs I1 and 43 are connected to the input terminalsof oscillator 5| and the prongs I1 and 44 are connected to the inputterminals of oscillator 52. The output terminals of the oscillators areconnected to the input circuit of a mixer stage 53 wherein thefrequencies of oscillators 5| and 52 are heterodyned, providing a lowfrequency beat signa] at the output terminals of said mixer stage. Byadjusting the trimmer condenser 2| in the manner above described, thebeat signal may be made to have any desired audio frequency. Since thecrystals have identical frequency-temperature characteristics, thederived beat frequency will remain constant in value over a considerablerange of temperatures.

Heretofore where crystal controlled oscillators have been employed toprovide a stable beat frequency, the crystals controlling the respectivebeating oscillators were physically in different environments, andalthough the crystals may have had identical temperature-frequencycharacter istics, variation in the respective temperatures of thecrystals has not been necessarily the same for both crystals. This hasproduced a substantial degree of instability of the beat frequency thusderived, especially where said beat frequency was of a low audio value.Where it was necessary to maintain stability of the audio frequencywithin close limits, the above described heterodyne method has beenunsuccessful because even a few degrees variation in temperature betweenthe crystals has resulted in many cycles of difference in the derivedaudio beat frequency. In the unit of the present invention, bothcrystals are in close physical contact with the metal ground plate I5,and although the temperature of said plate may vary, there is nodifference in the temperature of the crystals. Therefore, once the beatfrequency has been established by the adjustment of the trimmercondenser 2 I, the beat frequency will remain constant regardless ofexternal temperature conditions.

While a specic embodiment of a dual crystal assembly for use in beatfrequency oscillator circuits has been disclosed in the foregoingdescription, it will be understood that various modifications within thespirit of the invention may occur to those skilled in the art. Thereforeit is intended that no limitations be placed on the invention except asdefined by the scope of the appended claims What is claimed is:

1. A dual crystal holder comprising a base, an upstanding metal platemember secured to said base, a pair of insulating bars secured toopposing marginal portions of said plate member on one side thereof,said bars being formed with pairs of opposing projections defining withrespect to said plate member a pair of crystal-receiving cavities, saidplate member being formed between one pair of said opposing projectionswith an opening, and an adjustable impedance secured to the oppositeside of said plate member and having an adjusting element aligned withsaid opening.

2. A dual crystal holder comprising a base, an upstanding metal platemember secured to said base, a pair of insulating bars secured to theside marginal portions of said plate member at one face thereof, saidbars being formed with inwardly projecting opposing arms defining anup.. per and a lower crystal cavity, said plate member being formedbetween one set of opposing arms with an opening, and an adjustableimpedance secured to the opposite face of said plate member and havingan adjusting element aligned with said opening.

3. A dual crystal holder comprising a base, an upstanding metal platemember secured to said base, a pair of insulating bars secured to theside marginal portions of said plate member at one face thereof, saidbars being formed with inwardly projecting opposing arms defining anupper and a lower crystal-receiving cavity, said `plate member beingformed between the opposing arms intermediate the cavities with anopening, and an adjustable condenser secured to the opposite face ofsaid plate member and having an adjusting element aligned with saidopening.

4. A dual crystal holder comprising an insulating base, an upstandingmetal plate member secured to said base, a pair of vertical insulatingbars secured to the side marginal portions of said plate member at oneface thereof, said bars being formed with intermediate opposing arms andbottom opposing arms defining an upper rectangular space and a lowerrectangular space adjacent said one face of the plate member, said platemember being formed between the intermediate opposing arms with anopening, and an adjustable condenser secured to the opposite face ofsaid plate member and having an adjusting element projecting throughsaid opening,

5. A dual crystal unit comprising a base, an upstanding metal platemember secured to said base, a pair of vertical insulating bars securedto the side marginal portions of said plate member at one face thereof,said bars being formed with intermediate opposing arms and bottomopposing arms defining an upper rectangular space and a lowerrectangular space adjacent said one face of the plate member, said platemember being formed between the intermediate opposing arms with anopening, an adjustable condenser secured to the opposite face of saidplate member and having an adjusting element aligned with said opening,a crystal plate positioned in each space substantially in contact withsaid metal plate member. an electrode positioned in each space outwardlyadjacent the crystal plate therein, means secured to the outer surfacesof the bars in bridging relation to said spaces, and respective springspositioned between said means and the respective electrodes.

6. A dual crystal holder comprising a base, an upstanding ground platesecured to said base, insulating means secured to one side of saidground plate and formed to define two crystal-receiving cavities withthe ground plate as the inner wall of said cavities, said insulatingmeans also dening a space intermediate said cavities, said ground platebeing formed with an opening at said intermediate space, and anadjustable condenser secured to the opposite side of said ground plateand having an adjusting element aligned with said opening.

7. A dual crystal holder comprising a base, a ground plate secured tosaid base, insulating means secured to one side of said ground plate andformed to -dene two crystal-receiving cavities with the ground plate asthe inner wall of said cavities, said ground plate being formed with anopening adjacent said cavities, and an adjustable condenser secured tothe opposite side of said ground plate and having an adjusting elementaligned with said opening.

ROBERT J JAHRLING.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,688,714 Hund Oct, 23, 19282,031,768 Gebhard uu-,- Feb. 25. 1.936

